Also, our resident technical expert, Pinto, will have some great input I'm sure. He'll be along soon.
I've been called many things... but...
Hi Thommo 😉
Im going to assume that you bought one of the topless keggles that Malt Miller sold cheap a while back - because using kegs from "alternative sources" and cutting the top off them with an angle grinder is naughty and not to be condoned 😉
There are several ways you can go with this, depending in the main on the volume of the keg - 50L is standard, so you'll be needing at least 3kW of heating power to bring it to the boil in a reasonable time scale; You can easily get hold of 3kW immersion heater elements, but these are (a) not that cheap and (b) require a ~60mm hole to be cut into the side of the keg, which is convex and therefore difficult to seal to a flat based element.
My recommendation is to get a 40mm HSS or TCT Holesaw and one of these :
which will require you to cut a hole in the base of the keggle, which is flatter and more convenient (less likely to boil dry)
Additionally,the last 50L I converted, I added a 2kW boosting element :
Which means to reach boil, I can run 5kW of heating, giving a boil time of ~30 mins. These are a lot simpler, as they just require a pair of 12mm holes to be bored in the base,
Dont forget - drilling Stainless - use slow speed (speed 1 on a cordless driver), constant firm pressure (not too hard) and a proper cutting fluid (preferably) or plenty of WD40 - once you start the hole, dont stop till you're through !
On the electrical side, you're going to need a controller so you can maintain a healthy boil, but not one so violent the boil is unmanageable - read Adrian's excellent guide to his "Boil-o-Matic" for info on that 😉